Permanent magnets constituted of a rare earth element, a metal of the iron group and boron in the shape of a plate, such as plane, arcuate, semi-circular or crescent, and having magnetic anisotropy imparted by hot (or warm) plastic working have been industrially and domestically used. These permanent magnets are manufactured as will now be described below.
A raw material prepared by mixing a rare earth, a metal of the iron group and boron is melted and the molten magnet alloy thus obtained is jetted out onto a rotating roll of e.g. copper to form thereon a rapid-quenched flaky ribbon composed of nano-sized crystal grains. The magnet alloy powder obtained by rapid-quenching as described above is crushed into an appropriate particle diameter and cold pressed into a compact. The compact is hot or warm pressed into a body having higher density, and is then subjected to hot or warm plastic working to form a plate sized as desired and having magnetic anisotropy. Examples of the method for plastic working to impart magnetic anisotropy to the plate include (1) upsetting, (2) extrusion and (3) rolling. The magnet material subjected to plastic working is magnetized in the later step, whereby a practically useful permanent magnet having magnetic anisotropy is provided.
JP-A-9-129463, for example, generally describes the manufacture of a ring-shaped permanent magnet and the like by extrusion.